The following description relates generally to jib stowage, and in particular, to a jib coupling system for stowing a jib on a boom.
A lifting vehicle, such as a mobile crane, may have a telescoping boom comprised of a base section and one or more nested telescoping sections, extendable from, and retractable into the base section. In some boom configurations, a boom extension or jib may be affixed to a boom nose of the telescoping boom.
With reference to FIG. 1, in some mobile cranes, the jib 110 may be stowed along a side or top of the base section 112 of the boom 114 when not in use. In a stowed configuration, the jib 110 may be positioned having its base 116 generally adjacent to the boom nose 118, and its tip 120 positioned near a base 122 of the base section 112.
Typically, the jib extension will be stowed by way of a first stowage connection 124 at or near the tip 120 of the jib 110 and the base 122 of the base section 112, and a second stowage connection 126 positioned in an intermediate area between the jib tip 120 and the jib base 116, and between the base 122 of base section 112 and the boom nose 118.
In known jib stowage arrangements, the first stowage connection 124 may be released, as shown in FIG. 2, and the jib 110 can be pivoted about the second stowage connection 126 to move the a portion of the base 116 of the jib 110 into alignment with a portion of the boom nose 118. The respective portions of the jib base 116 and boom nose 118 may be connected to one another and serve as a pivot joint 128.
With respective portions of the jib base and boom nose 118 connected, the second stowage connection 126 may be released and the jib 110 may pivot around the pivot joint 128. Accordingly, the jib base 116 may be brought into alignment with the boom nose 118, along an axis of the boom 114, to secure the jib base 116 to the boom nose 118 and extend the boom 114.
One drawback to the known jib stowage arrangement above is that when moving the jib 110 from the stowed position to an operating position (i.e., connected to and installed at the boom nose 118), if the connection at the pivot joint 128 is not secure after the second stowage connection is released, the jib 110 may fall from the boom 114. Conversely, when moving from the jib 110 from the operable position to the stowed position, the jib 110 may fall from the boom if the second stowage connection 126 is not secured upon release of the pivot joint 128.
Efforts have been made to address the drawback described above. For example, U.S. Pat. No. 8,522,988 to Tanaka et al., includes a pair of pin retraction restriction means. In particular, Tanaka et al. discloses upper and lower pivot pins at a location corresponding to the pivot joint described above. The upper and lower pivot pins are movable away from one another to an extended position to couple the jib to the boom nose, and toward one another to a retracted position to decouple the jib from the boom nose. Tanaka et al. also discloses upper and lower coupling pins at a location corresponding to the second stowage connection described above. Similar to the pivot pins, the upper and lower coupling pins are movable away from one another to an extended position, whereby the jib may be coupled to the boom, and toward one another to a retracted position whereby the jib may be decoupled from the boom.
In Tanaka et al., one of the pin retraction restriction means includes a first restricting member and the other of the pin retraction restriction means includes a second restricting member. The first and second restricting members are pivoting arms urged by a spring into a gap formed between the pivot pins and coupling pins, respectively, when the pivot and coupling pins are in extended positions. Accordingly, the first and second restricting means may prevent retraction of the pivot pins and coupling pins.
In addition, the first and second restricting means are each connected, at an opposite end from the spring connection, to respective control cables. The control cable of the first restricting member is connected at an opposite end to the upper coupling pin, such that movement of the upper coupling pin to the extended position causes the control cable to pull the pivot arm of the first restricting member, against a biasing force, out of the gap between the upper and lower pivot pins. The control cable of the second restricting member is connected at an opposite end to the upper pivot pin, such that movement of the upper pivot pin to the extended position causes the control cable to pull the pivot arm of the second restricting member, against a biasing force, out of the gap between the upper and lower coupling pins.
Thus, movement of the coupling pins to the extended position causes the first restricting member to pivot out of gap between the upper and lower pivot pins, thereby allowing the pivot pins to retract. Similarly, movement of the pivot pins to the extended position causes the second restricting member to pivot out of a gap between the upper and lower coupling pins, thereby allowing the coupling pins to retract. In this manner, Tanaka et al. seeks to maintain a connection of at least one of the pivot pins or coupling pins to the boom at all times.
However, the arrangement described above is mechanically complex and requires numerous connections between moving parts. For example, each control cable is required to be connected at each end to either a pivot arm or a coupling or pivot pin to pull the cable in a predetermined direction. In addition, because of the number of moving parts, which are typically exposed to the environment, and the nature of working environments in which such a system is typically used, the pin retraction restriction system above may not be sufficiently durable, and could require frequent maintenance. This results in machine down time and increased service and maintenance costs.
Accordingly, it is desirable to provide a jib coupling system that maintains the jib in connection with the boom during movement from a stowed condition to an extended condition, and vice versa, with fewer components and reduced mechanical complexity